1. Field of the Invention
The present invention relates to a display device that comprises an element including a light emitting material sandwiched between electrodes (hereinafter referred to as a light emitting element), and to a manufacturing method of the display device. In particular, the invention relates to a display device using a light emitting material that generates EL (Electro Luminescence) (hereinafter referred to as an EL material).
2. Description of the Related Art
In recent years, an EL display device utilizing electro luminescence (hereinafter referred to as EL) has been developed. The EL display device, as well as a liquid crystal display device that has been in practical use, comprises pixels arranged in matrix to display images. Known as a driving method of pixels are a passive matrix method and an active matrix method using transistors. In either case, what attracts attention is that self-luminous type pixels each including an EL element formed of an EL material provide wide viewing angle and high contrast.
It is said that an EL element emits light through the following mechanism: a voltage is applied between a pair of electrodes that sandwich an organic compound layer, electrons injected from the cathode and holes injected from the anode are re-combined at the luminescent center of the organic compound layer to form molecular excitons, and the molecular excitons return to a ground state while releasing energy to cause the EL element to emit light. Excitation state includes a singlet exciton and a triplet exciton, and it is considered that luminescence can be made through either excitation state.
However, an EL material (particularly, an organic EL material) that mainly constitutes an EL element is characterized in that it is sensitive to moisture and degrades easily. Therefore, a sealing technology is an essential part of manufacturing of an EL display device. Known as a sealing structure is the one in which a sealing member is provided so as to surround a display area including EL elements and a sealing substrate is formed with the sealing member interposed therebetween (for example, see Patent Document 1).    [Patent Document 1] Japanese Patent Laid-Open No. 2003-255845